This invention relates to a coil that may be used, for example, as a component of a transformer or as a choke.
The applicant of the present application filed U.S. patent application Ser. No. 10/006,478 on Dec. 6, 2001, entitled xe2x80x9cHigh-Frequency Large Current Handling Transformerxe2x80x9d, which was published on Jun. 13, 2002 under US-2002-0070836-A1. The transformer disclosed in the U.S. application includes coil sheets or planar coil members 1, 2, 3, 4, 5 and 6 of metal, e.g. copper, as shown in FIG. 1. The metallic coil sheets 1, 2, 3, 4, 5 and 6 are formed in a rectangular shape with windows 1a, 2a, 3a, 4a, 5a and 6a in their center portions. One side of each coil sheet is cut to form a slit 1b, 2b, 3b, 4b, 5b, 6b therein. Tabs 1c and 1d extend outward from the portions facing across the slit 1b. Similarly, tabs 2c and 2d, 3c and 3d, 4c and 4d, 5c and 5d, and 6c and 6d extend outward from the portions of the respective sheet coils 2, 3, 4, 5 and 6 facing each other across the slits 2b, 3b, 4b, 5b and 6b. The tabs 1c, 2c, 3c, 4c, 5c and 6c provide winding start terminals, while the tabs 1d, 2d, 3d, 4d, 5d and 6d provide winding end terminals. The coil sheets 1, 2 and 3 are stacked, with the tabs 1d and 2c interconnected and with the tabs 2d and 3c interconnected, to thereby provide a primary winding of the transformer. Similarly, the coil sheets 4, 5 and 6 are stacked, with the tabs 4c, 5c and 6c interconnected and with the tabs 4d, 5d and 6d interconnected, to thereby provide a secondary winding. Insulating sheets 9, 10, 11 and 14 are disposed in such a manner that each coil sheets 1, 2 and 3 are sandwiched between two of the insulating sheets. An insulating sheet 17 is disposed on the stack of the coil sheets 4, 5 and 6 so as to sandwich them between the insulating sheets 17 and 14. The insulating sheets 9, 10, 11, 14 and 17 have center windows 9a, 10a, 11a, 14a and 17a, respectively. Two core halves of, for example, ferrite, 18 and 19 are used. The core halves 18 and 19 have center legs 18a and 19a, respectively, with grooves 18b and 18c, and 19b and 19c located on opposite sides of the respective legs 18a and 19a. Outward of the grooves 18b and 18c are outer legs 18d and 18e, respectively, and outward of the grooves 19b and 19c are outer legs 19d and 19e, respectively. The core halves 18 and 19 are combined in such a manner that the center legs 18a and 19a can be placed to extend through the center windows 1a-6a in the coil sheets 1-6 and the center windows 9a-14a and 17a in the insulating sheets 9-14 and 17.
In manufacturing this transformer, work for stacking the metallic coil sheets and the insulating sheets alternately is necessary, which increases the cost of the transformer. Furthermore, with this arrangement, the metallic coil sheets are exposed to air and, therefore, may be oxidized and rust after long use. In addition, in order to fulfill safety standards for transformers, it must be so arranged that a sufficient creepage distance can be kept even when the insulating sheets 9, 10, 11, 14 and 17 are displaced more or less with respect to is the metallic coil sheets. For that purpose, larger insulating sheets must be used, which makes transformers larger in size.
An object of the present invention is to provide a coil that requires fewer steps in manufacturing it, is hardly oxidized and is small in size.
A coil according to one embodiment of the present invention includes a coil section having a plurality of metallic coil sheets. The coil sheets are planar and each have a window in the center portion thereof. A slit is formed in each coil sheet, which extends from a location on the periphery of the window through the sheet to the outer periphery of the sheet. Connection terminals are formed on the sheet at locations facing each other across the slit. The coil sheets are stacked, and adjacent coil sheets are electrically connected with each other by the connection terminals. A core is disposed within the windows in the coil sheets. Each of the metallic coil sheets is individually coated completely with an insulating coating before the metallic coil sheets are stacked.
With the above-described arrangement, since each of the metallic coil sheet of the coil is individually pre-coated with an insulating coating, there is no need for placing an insulating sheet between adjacent coil sheets when the metallic coils sheets are stacked, which can reduce the manufacturing steps, which, in turn, can reduce the manufacturing cost. Furthermore, by covering the entire surface of each of the metallic coil sheets with an insulating coating, the metallic coil sheets are hardly oxidized and rusted. In addition, since each of the metallic sheets is individually pre-coated with an insulating coating, there is no need to take care to keep that insulating sheets are not displaced relative to the metallic coil sheets when the metallic coil sheets are stacked. Accordingly, it is not necessary to take such displacement into account when setting a creepage distance, and, therefore, the creepage distance can be set small. Then, the size of transformers can be reduced.
A plurality of coil sections may be used. The core is disposed to extend through the windows in the metallic coil sheets of the coil sections, so that the plural coil sections are inductively coupled with each other. This arrangement provides a transformer which can be manufactured at a low cost and hardly rust, and is small in size.
The insulating coatings may be formed by applying an insulative resin directly over the metallic coil sheet. Alternatively, an insulating film may be bonded to the metallic coil sheet to cover part of or the entirety of the surface of the metallic coil sheet before stacking the metallic coil sheets. The insulating resin may be used as an adhesive to bond the pre-formed insulating film to the metallic coil sheet.